This invention relates generally to dampers and more particularly to an improved damper blade having an air foil shape and a unique construction which permits the use of light gauge sheet metal while at the same time exhibiting ample strength to withstand the forces that are encountered in service of the damper.
Dampers have long been used in a variety of fluid handling applications to control the flow of various types of fluids. Typical uses of industrial dampers include the handling of process control fluids, the handling of fluids in power plants, and the handling of high speed fan discharge streams. Industrial dampers are usually subjected to relatively high pressures and must have considerable strength in order to be capable of withstanding the forces that are applied to them.
The damper construction normally includes a rigid frame which defines a flow passage controlled by a plurality of damper blades that pivot between open and closed positions. The blades are often interconnected by a linkage which moves all of them in unison to control the fluid flow rate in accordance with the damper blade position. Although flat damper blades are often used, it has long been recognized that airfoil shapes can be used to enhance the fluid flow. Airfoil blades are thickest in the center at the pivot axis and taper toward each edge to present an aerodynamically efficient shape which minimizes turbulence and other undesirable effects such as noise generation and stresses on the flow passage and other components of the fluid handling system.
In the past, airfoil shaped blades have been formed for the most part by extrusion processes. Extrusion techniques have the advantage of allowing the airfoil shape to be extruded in long sections and then cut into individual damper blades having the required lengths. However, the extrusion process is disadvantageous in a number of respects, most notably in its relatively high costs, relatively high energy requirements, and limitations in the materials that can be used to construct the blades.
It has been found that sheet steel can be bent into an airfoil shape at a reduced cost in comparison to the extrusion of materials such as aluminum. However, in order to provide the sheet metal damper blade with sufficient strength to withstand the considerable forces that are encountered, it has been necessary to use relatively heavy gauge sheet metal to construct the damper blade. This increases both the weight and cost of the blade. An additional problem with sheet metal blades is that the damper axle must either extend completely through the blade or the blade must be reinforced by a full length tube in order to adequately support the blade and maintain it properly centered on the axle. Both of these alternatives require added material, and the cost and weight are increased accordingly.